Abstract(Sherlock S, Way M, Tabah A. Audit of practice in Australian and New Zealand hyperbaric units on the incidence of central nervous sytem oxygen toxicity. Diving and Hyperbaric Medicine. 2018 June;48(2):73–78. doi. 10.28920/dhm48.2.73-78. PMID: 29888378.)Introduction: Central nervous system oxygen toxicity (CNS-OT) is an uncommon complication of hyperbaric oxygen treatment (HBOT). Different facilities have developed local protocols in an attempt to reduce the risk of CNS-OT. This audit was performed to elucidate which protocols might be of benefit in mitigating CNS-OT and to open discussion on adopting a common protocol for Treatment Table 14 (TT14) to enable future multicentre clinical trials.Methods: Audit of CNS-OT events between units using different compression profiles for TT14, performed at 243 kPa with variable durations of oxygen breathing and ‘air breaks’, to assess whether there is a statistical diference between protocols. Data were collected retrospectively from public and private hyperbaric facilities in Australia and New Zealand between01 January 2010 and 31 December 2014.Results: Eight of 15 units approached participated. During the five-year period 5,193 patients received 96,670 treatments. There were a total of 38 seizures in 33 patients when all treatment pressures were examined. In the group of patients treated at 243 kPa there were a total of 26 seizures in 23 patients. The incidence of seizure per treatment was 0.024% (2.4 per 10,000 treatments) at 243 kPa and the risk per patient was 0.45% (4.5 in 1,000 patients). There were no statistically significant differences between the incidences of CNS-OT using different TT14 protocols in this analysis.Conclusion: HBOT is safe and CNS-OT is uncommon. The risk of CNS-OT per patient at 243 kPa was 1 in 222 (0.45%; range 0−1%) and the overall risk irrespective of treatment table was 0.6% (range 0.31−1.8%). These figures are higher than previously reported as they represent individual patient risk as opposed to risk per treatment. The wide disparity of facility protocols for a 243 kPa table without discernible influence on the incidence of CNS-OT rates should facilitate a national approach to consensus.

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(Livingstone DM, Lange B. Rhinologic and oral-maxillofacial complications from scuba diving: a systematic review with recommendations. Diving and Hyperbaric Medicine. 2018 June;48(2):79–83. doi: 10.28920/dhm48.2.79-83. PMID: 29888379.)Rhinologic and oral maxillofacial complications from scuba diving are common, representing approximately 35% of head and neck pathology related to diving. We performed a systematic and comprehensive literature review on the pathophysiology, diagnosis, and treatment of rhinologic and oral maxillofacial pathology related to diving. This included complications due to sinus barotrauma, barodontalgia, odontocrexis, temporomandibular joint dysfunction, partially dentulous patients, and considerations for patients following major head and neck surgery. Of 113 papers accessed, 32 were included in the final synthesis. We created a succinct summary on each topic that should inform clinical decision making by otolaryngologists, dive medicine specialists and primary care providers when faced with pathology of these anatomic sub-sites.

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(Doolette DJ, Mitchell SJ. In-water recompression. Diving and Hyperbaric Medicine. 2018 June;48(2):84–95. doi: 10.28920/dhm48.2.84-95. PMID: 29888380.)Divers suspected of suffering decompression illness (DCI) in locations remote from a recompression chamber are sometimes treated with in-water recompression (IWR). There are no data that establish the benefits of IWR compared to conventional first aid with surface oxygen and transport to the nearest chamber. However, the theoretical benefit of IWR is that it can be initiated with a very short delay to recompression after onset of manifestations of DCI. Retrospective analyses of the effect on outcome of increasing delay generally do not capture this very short delay achievable with IWR. However, in military training and experimental diving, delay to recompression is typically less than two hours and more than 90% of cases have complete resolution of manifestations during the first treatment, often within minutes of recompression. A major risk of IWR is that of an oxygen convulsion resulting in drowning. As a result, typical IWR oxygen-breathing protocols use shallower maximum depths (9 metres’ sea water (msw), 191 kPa) and are shorter (1–3 hours) than standard recompression protocols for the initial treatment of DCI (e.g., US Navy Treatment Tables 5 and 6). There has been no experimentation with initial treatment of DCI at pressures less than 60 feet’ sea water (fsw; 18 msw; 286 kPa; * see footnote) a since the original development of these treatment tables, when no differences in outcomes were seen between maximum pressures of 33 fsw (203 kPa; 10 msw) and 60 fsw or deeper. These data and case series suggest that recompression treatment comprising pressures and durations similar to IWR protocols can be effective. The risk of IWR is not justified for treatment of mild symptoms likely to resolve spontaneously or for divers so functionally compromised that they would not be safe in the water. However, IWR conducted by properly trained and equipped divers may be justified for manifestations that are life or limb threatening where timely recompression is unavailable.

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Abstract(Pollock NW, Gant N, Harvey D, Mesley P, Hart, J, Mitchell SJ. Storage of partly used closed-circuit rebreather carbon dioxide absorbent canisters. Diving and Hyperbaric Medicine. 2018 June;48(2):96–101. doi: 10.28920/dhm48.2.96-101. PMID: 29888381.)Introduction: Diving rebreathers use “scrubber” canisters containing soda lime to remove carbon dioxide (CO2) from the expired gas. Soda lime has a finite ability to absorb CO2. We undertook an experiment to determine whether the manner of storage of a partly used scrubber affected subsequent CO2 absorption.Methods: An Evolution Plus™ rebreather was mechanically ventilated in a benchtop circuit. Respiratory minute volume was 45 L∙min-1 and CO2 was introduced to the expiratory limb at 2 L∙min-1. The scrubber canister was packed with 2.64 kg of Sofnolime 797™. Scrubbers were run in this circuit for 90 minutes then removed from the rebreather and stored in packed form under one of three conditions: “open” (unsealed) for 28 days (n = 4); vacuum “sealed” in an airtight plastic bag for 28 days (n = 5); or open overnight (n = 5). Following storage the scrubber canisters were placed back in the rebreather and run as above until the PCO2 in the inspired gas exceeded 1 kPa. The total duration of operation to reach this end-point in each storage condition was compared.Results: The mean run times to reach an inspired CO2 of 1 kPa were 188, 241, and 239 minutes in the open-28-day, the sealed-28-day and the open-overnight storage conditions, respectively.Conclusion: Rebreather divers should consider placing partially used soda lime scrubber canisters in vacuum-sealed plastic bags if storing them for longer periods than overnight. If a partially used scrubber canister is to be used again the next day then the storage modality is unlikely to influence scrubber efficacy.

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Abstract(Lie SA, Loy ST, Lee CC, Kim SJ, Soh CR. Performance of the Oxylog® 1000 portable ventilator in a hyperbaric environment. Diving and Hyperbaric Medicine. 2018 June;48(2):102–106. doi. 10.28920/dhm48.2.102-106. PMID: 29888382.)Introduction: The management of mechanically ventilated patients in the hyperbaric environment requires knowledge of how the physical properties of gases change under pressure and how this affects the operation of the ventilator. The primary objective of this study was to test the performance of the Dräger Oxylog 1000® ventilator in a hyperbaric environment.Methods: Each of two ventilators was connected to a mechanical test lung system with an in-built pressure gauge. We used a Wright’s respirometer to measure the tidal volumes. The same ventilator settings were tested under varying environmental pressures from ambient (101.3 kPa) to 18 meters’ sea water (284 kPa) in a multiplace hyperbaric chamber.Results: A decrease was found in tidal volume, decrease in airway pressure and increase in respiratory rate delivered by the Dräger Oxylog 1000 portable ventilator with increasing pressures to 284 kPa.Discussion: These findings can be explained by the operating principles of the Oxylog 1000, which is a time-controlled, constant-volume ventilator that functions as a flow chopper. Even between the two Oxylog 1000 ventilators tested there were different absolute changes in tidal volume, airway pressures and respiratory rates at various depths. Hence, the trend of changes in these variables is probably more important than absolute values.Conclusion: In summary, understanding the trend of changes in ventilator variables will allow clinicians to make appropriate corrections in ventilator settings and carefully monitor adequacy of ventilation to prevent adverse ventilator-associated events. The Dräger Oxylog 1000 portable ventilator is an adequate back-up ventilator for use with straight-forward, ventilator-dependent patients undergoing hyperbaric treatment.

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Abstract(Teoh SY, Vangaveti VN. Repeated hyperbaric exposure and glass ampoule safety. Diving and Hyperbaric Medicine. 2018 June;48(2):107–109. doi: 10.28920/dhm48.2.107-109. PMID: 29888383.)Introduction: It has been our institution’s policy to not place glass medication ampoules inside our hyperbaric chamber for fear of rupture. There is only a small and conflicting amount of data as to whether lass ampoules are safe for use under hyperbaric conditions.Objectives: The primary objective of this study was to test the safety and usability of glass medication ampoules inside a hyperbaric chamber.Methods: Repetitive, rapidly staged compressions and decompressions were performed on multiple different glass medication ampoules inside the medical lock of a medical hyperbaric chamber. Medication ampoules of varying sizes (1 ml to 10 ml) of medications that may be required in a hyperbaric emergency were assessed. The ampoules were rapidly compressed100 times to pressures of 142 kPa, 183 kPa, 300 kPa, 405 kPa and 507 kPa. They were then dropped from a height of 30 cm while compressed at 507 kPa and then half the ampoules were opened while pressurized at 507 kPa.Results: No ampoules were broken during compression or decompression. No ampoules broke when dropped from 30 cm onto the chamber floor. All ampoules opened at a pressure of 507 kPa functioned normally. No lids/ampoules shattered upon opening.Conclusion: This study suggests that glass medication ampoules appear to be safe for use inside a medical hyperbaric chamber at routine treatment pressures.

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(Hacene B, Draulans N, Theys T. Problems with an intrathecal pump in a paraplegic scuba diver. Diving and Hyperbaric Medicine. 2018 June;48(2):110–111. doi. 10.28920/dhm48.2.110-111. PMID: 29888384.)Scuba diving with an intrathecal baclofen pump is encouraged for people with spinal cord injury who are suffering from spasticity. However, the diving depth is limited to 10 metres in this context. Proper physician and patient education in this respect is mandatory since non-compliance can lead to an irreversible loss of drug reservoir capacity due to collapse of the bottom shield. We report such an incident in a paraplegic diver diving to depths down to 30 metres’ water.

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(Omar AR, Ibrahim M, Hussein A. Acute ophthalmic artery occlusion in decompression illness with underlying anterior cerebral artery A1 segment hypoplasia. Diving and Hyperbaric Medicine. 2018 June;48(2):112–113. doi: 10.28920/dhm48.2.112-113. PMID: 29888385.)A diver presented with total loss of vision in the left eye and right hemiparesis following a routine no-stop scuba dive to 20 metres’ depth. A diagnosis of decompression illness (DCI) with acute ophthalmic artery air embolism and left carotid artery insult causing acute anterior circulatory ischaemia was made. He underwent seven hyperbaric treatments leading to a full recovery. Magnetic resonance angiography revealed an underlying left anterior cerebral artery A1 segment hypoplasia. Making a prompt diagnosis and early hyperbaric oxygen treatment are crucial to halt further tissue damage from ischaemia in central nervous system DCI. In this case, the finding of a left A1 anterior cerebral artery segment hypoplasia variant may have increased the severity of DCI due to deficient collateral circulation.

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